Catheter ablation has proven to be an effective treatment option in patients suffering from symptomatic persistent atrial fibrillation (AF). Catheter ablation consists of two major steps: (1) Isolation of pulmonary veins to abolish the trigger of atrial fibrillation and (2) modification of left atrial and eventually right atrial substrate by ablation of complex fractionated atrial electrograms (CFAE). CFAE are mainly found at the ostia of the pulmonary veins, around the left atrial appendage, at the mitral annulus and the septum.